The boys can't wait for Halloween. Especially Alvin, who gets to scare people without getting in trouble. As the Chipmunks go out to Trick or Treat, Theodore as a chef, Simon as his favorite math star, and Alvin as a superhero, thei think it'll be the best night ever. But when Alvin suddenly disappears, the Seville's don't know what to do. The police didn't find him, and they told Dave that they suspect he was mysteriously killed by something. Simon and Theodore grieve over their brother's death. But, when strange things start happening, like there being a lump in Alvin's bed at night when nothing is there, milk pouring itself, and Alvin's guitar playing every night at 6:00, by itself. As the boys and Dave start to get freaked out, Simon comes up with a question that gets them all thinking. Could what was happening to the house tie in with Alvin's sudden missing and death?